A box tray of the general type utilized, with a small modification, by the present invention, was disclosed in my U.S. Pat. No. Re. 26,386, May 7, 1968. My U.S. Pat. No. 3,750,936 discloses portions of the tray, in a two tier stack, and also a metal wire clip serving as a stacking guide and handle by which a two tier stack of the trays may be conveniently carried, and whose upper extremities may be bent over to hold a cover sheet in place. See also my U.S. Pat. No. 2,971,232, showing a clip with downwardly spreading leg portions, the clip being insertable from below, and supporting each tray from below.
Problems encountered with these facilities have included undue cost of the metal clips, and insecurity of the cover sheets when bound in the simple manner of the prior art. Objectives of the invention include the provision of a unique and improved clip, fabricated from plastics material, unique and improved coaction between the clip and container, and a novel and improved interlock between a formation on the upper portion of the uppermost clip of a stack of trays with a unique, effective and improved locking conformation formed in the cover sheet.